High pressure electric discharge lamp with rare-gas filling



Nov. 20, 1962 H. GRABNER 3,065,370

HIGH PRESSURE ELECTRIC DISCHARGE LAMP WITH RARE-GAS FILLING Filed July 18, 1960 2 Sheets-Sheet J Fig.1

Nov. 20, 1962 H. GRABNER HIGH PRESSURE ELECTRIC DISCHARGE LAMP WITH RARE-GAS FILLING Filed July 18, 1960 2 Sheets-Sheet 2 amount of mercury Fig. 2

INVENTO R United States Patent Ofitice 3,hfi5,37 Patented Nov. 20, 1%62 3,065,370 HIGH PRESSURE ELECTRIC DISCHARGE LAMP WiTH RARE-GAS FILLING Horst Grahner, Berlin-Zehlendorf, Germany, assignor to Patent-Treuhand-Gesellschaft fur Elektrische Giuhlampen m.h.H., Munich, Germany Filed July 18, 196;), Ser. No. 43,688 Claims priority, application Germany July 22, 1959 4 Claims. (Cl. 313185) This invention relates to high pressure gaseous discharge lamps for continuous operation, as distinguished from pulsed operation. It relates more particularly to xenon discharge lamps the electrode distance of which amounts at least to double the inside tube diameter, wherein the discharge are is stabilized by the influence of the Wall of the discharge envelope. The bulb material consists of quartz glass or other transparent or translucent material of still higher thermal load capacity than quartz glass. Artificial cooling of the discharge tube being omitted, the lamps have an average input concentration in the discharge which lies between about and 200 watts per cubic centimeter and have a filling pressure of the rare gas filling reduced to a lamp without dead space between 5 and 350 mm. mercury. The lamp is operated with a low gradient and a low current density.

It is the object of this invention to improve the described high pressure gaseous discharge lamps.

it is another object of the invention to provide a high pressure gaseous discharge lamp of the described type with improved luminous efficiency.

It is still another object of the invention to provide a high pressure gaseous discharge lamp of the described type with increased voltage gradient of the discharge are.

The aforesaid objects of the present invention and other objects which will become apparent when the description proceeds are accomplished by providing a high gaseous discharge lamp of the type set forth with a small amount of mercury of 0.0l0.7 milligram per cubic centimeter in addition to the rare gas filling in the discharge envelope, the current density of the discharge thereby exceeding 2 amperes per square centimeter.

Heretofore it was known to add metal vapors, for instance mercury, to the rare-gas filling of the well-known ball-shaped high-pressure discharge lamps wherein the electrode spacing amounts only to a fraction of the bulb diameter. These lamps contain a high-pressure filling of rare gas of several atmospheres and are operated without wall stabilization. Besides, high-pressure discharge lamps with rare-gas filling having an addition of mercury are known, wherein the electrode spacing amounts to several centimeters with an inside diameter of the lamp bulb of a few millimeters. But in these lamps, too, the rare gas has already a pressure of several atmospheres at room temperature. Apart from the lamps mentioned above, there have been constructed oblong high-pressure gaseous discharge lamps containing mercury and a rare gas, such as xenon, as starting gas and being designed for the exposure of photographic papers. These lamps have relatively low nominal ratings of about 3 kilowatts or less and are operated with low amperages so as to keep the average current density below 1 ampere per cm. In accordance with their use, the lamps are thus dimensioned that a luminous efiiciency of long-wave ultraviolet of high stability is attained.

Contrary to the hitherto known long-arc mercury lamps having xenon as starting gas and being designed for a maximum nominal rating up to 3 kilowatts and being operated at low amperages, the lamp-type according to the invention is designed for high-wattage lamps of higher nominal rating. The upper limit of the amount of mercury to be added, i.e. 0.7 milligram per cm. is due to the structural designs of lamps down to nominal ratings of 3 kilowatts, since with decreasing nominal rating and smaller tube diameter a greater amount of mercury is necessary in order to obtain an optimum light output.

The characteristic feature or" the type of lamp set forth is, that in spite of the relatively low filling pressure of the rare gas of less than 350 mm. mercury the lamps show real high-pressure characteristics. This means that the gas temperature which amounts to about 6500 to 9000" K. is only a little less than the electron temperature. Compared with lamps of e.g. high pressure, low amperages, small discharge diameters, high wattage concentrations known prior thereto, with lamps according to the main patent there are obtained approximately even luminous efficiencies with lower wattage concentrations, low pressure and wall stabilization, provided higher amperages and larger arc diameters are used.

Now, it according to the invention mercury is added to the rare-gas filling of the lamps, the high-pressure characteristic of the lamps is maintained, i.e. the temperature of approximately 7000" K. as stated for lamps with an entire noble gas filling is not changed. The gradient is increased by the addition of mercury; the luminous effciency is not only maintained but is also increased. Moreover, with lamps according to the invention it proved new and surprising that the progress in increase in luminous eiliciency is completely different from the hitherto known long-arc mercury lamps with xenon as filling gas. in the last mentioned lamps the luminous efiiciency increases continuously with increasing pressure, i.e. with increasing amounts of mercury per cm. Contrary thereto, in lamps according to the invention initially there takes place a rapid increase in luminous efiiciency but chan es over already after adding small amounts of mercury, i.e. at relatively low operating pressure, to a range of almost constant, maximum efficiency.

For further objects and advantages and for a detailed description of the invention, attention is now directed to the following description and accompanying drawing illustrating preferred embodiments of the invention. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

FIG. 1 is a front elevation view of an electric high pressure gaseous discharge lamp embodying the invention with the front portion of the envelope cut away to show more clearly the arrangement of the electrodes and the diaphragms.

FIG. 2 is a graph illustrating the variation of luminous eificiency and of the voltage gradient with the amount of mercury added for one special embodiment of the inven tion. Referring to the drawing and more particularly to PEG. 1, there is shown an electric high pressure gaseous discharge lamp for A.C. operation on 220 volts. The tubular envelope 1 made from quartz glass, having a diameter d of 30 mm. and a length of about cm. The cylindrical electrode bodies 2 and 3 of thoriated tungsten are about one third of the tube diameter. in front of the electrodes are mounted the perforated quartz glass discs 4 and 5 as protective diaphragms. The lamp contains a filling of Xenon as rare gas at a filling pressure of 100 mm. mercury corresponding to a reduced filling pressure of approximately 70 mm. mercury and an addition of mercury. With an arc loading of watts per cm. maintained constant, there results a nominal rating of approximately 20 kilowatts. The current. density amounts to about 6 amperes per crn.

In FIG. 2 as is to be learned from curve B of the graph, the gradient increases with increasing mercury concentration. Within the range of the increasing voltage gradient the luminous intensity viz. the luminous flux both increase at first rapidly according to curve A of the graph. With a filling of only 0.2 milligram mercury per em this filling corresponding to a mercury operating pressure of only about 200 mm. mercury, the luminous eficiency attains its peak. On further increase of mercury added, practically the luminous eificiency does not increase further.

According to the invention there results a xenon-mercury discharge of low pressure and high gas-temperature with a luminous efiiciency as in the case of a high-pressure mercury vapor discharge lamp. Manufacture of these lamps for arbitrarily high wattages is possible. Whilst with lamps having a filling of pure rare gas and high nominal rating, e.g. 65 kilowatts, a luminous flux exceeding two million lumens is obtained, it is possible to obtain more luminous flux at the same wattage with lamps according to the invention and having mercury added to the rare-gas filling.

While in accordance with the patent statutes a preferred embodiment of the present invention has been illustrated and described in detail it is to be particularly understood that the invention is not limited thereto or thereby.

I claim:

1. An electric high pressure gaseous discharge lamp for continuous operation comprising an elongated envelope of a radiation transmitting material having a temperature resistance similar to quartz, a pair of electrodes mounted in said envelope at a distance apart amounting to at least double the inside diameter of the envelope, and an ionizable filling within said envelope comprising an inert gas from the group consisting of xenon, krypton, argon, neon, helium and mixtures thereof at a filling pressure equivalent to a pressure in the range of 5 to 350 millimeters of mercury in a lamp Without dead space and an amount of mercury in the range of 0.01 to 0.7 milligram per cubic centimeter lamp volume, said l'a'rn'p having an input watt- ,age concentration in the range of 5 to 200 watts per cubic centimeter and a current density of the discharge amounting to more than 2 amperes per square centimeter and being so proportioned with respect to distance apart of the electrodes and inside diameter of the envelope that with the said input concentration and with the said filling pressure in the absence of any artificial cooling a wall stabilized discharge is achieved.

2. An electric high pressure gaseous discharge lamp as defined in claim 1 wherein the input wattage concentration in the discharge is in the range of approximately 10 to References Cited in the file of this patent UNITED STATES PATENTS Gottschalk Aug. 26, 1958 Schirmer et a1. Feb. 9, 1960 

1. AN ELECTRIC HIGH PRESSURE GASEOUS DISCHARGE LAMP FOR CONTINUOUS OPERATION COMPRISING AN ELONGATED ENVELOPE OF A RADIATION TRANSMITTING MATERIAL HAVING A TEMPERATURE RESISTANCE SIMILAR TO QUARTZ, A PAIR OF ELECTRODES MOUNTED IN SAID ENVELOPE AT A DISTANCE APART AMOUNTING TO AT LEAST DOUBLE THE INSIDE DIAMETER OF THE ENVELOPE, AND AN IONIZABLE FILLING WITHIN SAID ENVELOPE COMPRISING AN INERT GAS FROM THE GROUP CONSISTING OF XENON, KRYPTON, ARGON, NEON, HELIUM AND MIXTURES THEREOF AT A FILING PRESSURE EQUIVALENT TO A PRESSURE IN THE RANGE OF 5 TO 350 MILLIMETERS OF MERCURY IN A LAMP WITHOUT DEAD SPACE AND AN AMOUNT OF MERCURY IN THE RANGE OF 0.01 TO 0.7 MILLIGRAM PER CUBIC CENTIMETER LAMP VOLUME, SAID LAMP HAVING AN INPUT WATTAGE CONCENTRATION IN THE RANGE OF 5 TO 200 WATTS PER CUBIC CENTIMETER AND A CURRENT DENSITY OF THE DISCHARGE AMOUNTING TO MORE THAN 2 AMPERES PER SQUARE CENTIMETER AND BEING SO PROPORTIONED WITH RESPECT TO DISTANCE APART OF THE ELECTRODES AND INSIDE DIAMETER OF THE ENVELOPE THAT WITH THE SAID INPUT CONCENTRATION AND WITH THE SAID FILLING PRESSURE IN THE ABSENCE OF ANY ARTICIFIAL COOLING A WALL STABILIZED DISCHARGE IS ACHIEVED. 